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KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (6)

Status: upstream: reported on 2026/03/12 15:26
Subsystems: net
[Documentation on labels]
Reported-by: syzbot+b44f2bbe286b9355c563@syzkaller.appspotmail.com
First crash: 64d, last: 36d
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
9b90f99c-6615-476d-baf9-c80b52368987 repro KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (6) 2026/03/06 07:23 2026/03/06 07:23 2026/03/06 07:29 31e9c887f7dc24e04b3ca70d0d54fc34141844b0
468a4ffd-c8e1-4da3-a072-b53524c115a9 assessment-kcsan Benign: ✅  Confident: ✅  KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (6) 2026/01/16 06:08 2026/01/16 06:08 2026/01/16 06:11 a9d6a79219801d2130df3b1a792c57f0e5428e9f
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [net?] KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (6) 1 (2) 2026/03/12 15:30
Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (4) net 6 1 735d 735d 0/29 auto-obsoleted due to no activity on 2024/04/20 09:12
upstream KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (3) net 6 2 953d 936d 0/29 auto-obsoleted due to no activity on 2023/09/15 15:27
upstream KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (5) net 6 1 216d 216d 0/29 auto-obsoleted due to no activity on 2025/10/12 11:19
upstream KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue (2) net 6 1 1545d 1545d 0/29 auto-closed as invalid on 2022/01/31 12:56
upstream KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue net 6 1 1858d 1858d 0/29 auto-closed as invalid on 2021/03/24 02:52

Sample crash report:
==================================================================
BUG: KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue

write to 0xffff88811d5ccc00 of 8 bytes by interrupt on cpu 0:
 __ptr_ring_zero_tail include/linux/ptr_ring.h:259 [inline]
 __ptr_ring_discard_one include/linux/ptr_ring.h:291 [inline]
 __ptr_ring_consume include/linux/ptr_ring.h:311 [inline]
 __skb_array_consume include/linux/skb_array.h:98 [inline]
 pfifo_fast_dequeue+0x770/0x8f0 net/sched/sch_generic.c:770
 dequeue_skb net/sched/sch_generic.c:297 [inline]
 qdisc_restart net/sched/sch_generic.c:402 [inline]
 __qdisc_run+0x189/0xc80 net/sched/sch_generic.c:420
 qdisc_run include/net/pkt_sched.h:120 [inline]
 net_tx_action+0x379/0x590 net/core/dev.c:5793
 handle_softirqs+0xb9/0x280 kernel/softirq.c:622
 do_softirq+0x45/0x60 kernel/softirq.c:523
 __local_bh_enable_ip+0x70/0x80 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 bpf_test_run+0x2db/0x620 net/bpf/test_run.c:426
 bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721
 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246
 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339
 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88811d5ccc00 of 8 bytes by task 22632 on cpu 1:
 __ptr_ring_produce include/linux/ptr_ring.h:106 [inline]
 ptr_ring_produce include/linux/ptr_ring.h:129 [inline]
 skb_array_produce include/linux/skb_array.h:44 [inline]
 pfifo_fast_enqueue+0xd5/0x2c0 net/sched/sch_generic.c:741
 dev_qdisc_enqueue net/core/dev.c:4144 [inline]
 __dev_xmit_skb net/core/dev.c:4188 [inline]
 __dev_queue_xmit+0x6a4/0x1f20 net/core/dev.c:4795
 dev_queue_xmit include/linux/netdevice.h:3384 [inline]
 __bpf_tx_skb net/core/filter.c:2153 [inline]
 __bpf_redirect_common net/core/filter.c:2197 [inline]
 __bpf_redirect+0x862/0x990 net/core/filter.c:2204
 ____bpf_clone_redirect net/core/filter.c:2487 [inline]
 bpf_clone_redirect+0x20c/0x290 net/core/filter.c:2450
 bpf_prog_53f18857bc887b09+0x22/0x2a
 bpf_dispatcher_nop_func include/linux/bpf.h:1402 [inline]
 __bpf_prog_run include/linux/filter.h:723 [inline]
 bpf_prog_run include/linux/filter.h:730 [inline]
 bpf_test_run+0x29d/0x620 net/bpf/test_run.c:423
 bpf_prog_test_run_skb+0x9a4/0xef0 net/bpf/test_run.c:1159
 bpf_prog_test_run+0x204/0x340 kernel/bpf/syscall.c:4721
 __sys_bpf+0x52e/0x7e0 kernel/bpf/syscall.c:6246
 __do_sys_bpf kernel/bpf/syscall.c:6341 [inline]
 __se_sys_bpf kernel/bpf/syscall.c:6339 [inline]
 __x64_sys_bpf+0x41/0x50 kernel/bpf/syscall.c:6339
 x64_sys_call+0x10cb/0x3020 arch/x86/include/generated/asm/syscalls_64.h:322
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x12c/0x370 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0xffff888104a93a00 -> 0x0000000000000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 UID: 0 PID: 22632 Comm: syz.0.4135 Tainted: G        W           syzkaller #0 PREEMPT(full) 
Tainted: [W]=WARN
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/02/13 12:39 upstream 37a93dd5c49b 6a673c50 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue
2026/01/16 06:08 upstream 603c05a1639f d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-kcsan-gce KCSAN: data-race in pfifo_fast_dequeue / pfifo_fast_enqueue
* Struck through repros no longer work on HEAD.